Tetragnathidae Menge 1866

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Introduction

The orb weaving spider family Tetragnathidae includes about 1000 described species in 51 genera (Platnick, 2009). The family is most diverse in the tropical regions and many species still remain unknown to science. Many tetragnathids are associated with some of the world's most important and fragile ecosystems, wetlands and river ecosystems, often building their orb webs very close to the water surface. Although many species live in relatively humid conditions, there are also others that thrive in dry climates. A good number of species are known from caves, such as many of the members of the genus Meta. Species in the genus Tetragnatha provide a striking example of dispersion abilities and ecological plasticity. With more than 340 described species and a distribution range that spans from the Arctic to the most remote oceanic islands Tetragnatha is one of the champions of the animal kingdom.

Characteristics

Most tetragnathid males have conspicuously enlarged chelicerae, often armored with numerous teeth. Some of these teeth, along with specialized cheliceral apophyses, play an important role during courtship and copulation as they are involved in a behavior known as cheliceral clasp (Bristowe, 1958; Eberhard and Huber, 1998). Other characters common to most tetragnathids are the close association of the embolus and conductor in the male palp, the presence of conspicuous trichobothria on the fourth leg femur and juxtaposed lateral eyes. Nevertheless, morphological features vary considerably within the family and there are several species that differ from the typical tetragnathid morphology. Females of the majority of tetragnathid genera have entelegyne genitalia, but the members of the subfamily Tetragnathinae provide a remarkable exception: all tetragnathines are secondarily haplogyne.

Discussion of Phylogenetic Relationships

The first phylogenetic analysis of tetragnathids was that of Levi (1980) which did not recover Tetragnathidae monophyly, but his taxon and character sample was very limited. The first to demonstrate the monophyly of Tetragnathidae using numerical cladistic methods was Coddington (1990). He was also the first to suggest that tetragnathids are more closely related to other araneoid lineages than Araneidae. All subsequent cladistic analyses that included tetragnathid representatives have recovered the monophyly of the family. Earlier phylogenetic analyses of tetragnathids and their relatives relied heavily on morphological data and included a smaller fraction of behavioral characters (Coddington, 1990; Hormiga et al., 1995; Griswold et al., 1998). All these earlier studies included Nephila and its relatives in the tetragnathid subfamily Nephilinae, together with the genus Phonognatha. Kuntner (2005) elevated the subfamily Nephilinae to family rank and suggested that Deliochus and Phonognatha may not belong in Tetragnathidae. Later on Kuntner et al. (2008) formally transferred Deliochus and Phonognatha to the family Araneidae.

Recent and ongoing work on tetragnathids has further advanced our knowledge about the phylogenetic structure of this family. Álvarez-Padilla (2007) and Dimitrov and Hormiga (2009) have used extensive morphological and behavioral data to study tetragnathid phylogeny. More recently, Álvarez-Padilla et al. (2009) have added multigene DNA sequence data to the morphological and behavioral evidence. We present here the results of their study as the most current phylogenetic classification for Tetragnathidae. Álvarez-Padilla et al.'s (2009) study confirmed that Nephila and its relatives do not belong into Tetragnathidae (as it had been proposed by some earlier classifications, such as Eugene Simon's), but their exact phylogenetic placement remains unclear.

Page: Tree of Life
Tetragnathidae Menge 1866.
Authored by
Dimitar Dimitrov and Gustavo Hormiga.
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